In a modern day motor vehicle, efforts have been made to soundproof the passenger compartment. One result of such soundproofing is that the driver may be unable to hear approaching emergency vehicle having its audio siren turned on. Alternatively, the playing of a radio or stereo at loud volume may make the driver unable to hear an approaching emergency vehicle with the audio siren on. A hearing impaired driver may be unable to hear an approaching emergency vehicle with its siren on. Two or more emergency vehicles of the same or different disciplines, responding to the same or to different dispatchers, approaching the same intersection may not be able to hear the other approaching emergency vehicle due to the audible sound of his or her own siren and hence is unaware of the presence of another emergency vehicle responding to the same or a different emergency call.
If the emergency vehicle is using a silent approach, motorists in the vicinity will not be aware of the presence of the emergency vehicle approaching an intersection if the siren is not turned on. An emergency vehicle (or other patient transport vehicle) transporting a patient and not using an audio siren poses a risk to other motorists who will be unaware of the approaching emergency vehicle.